There exists a category of eyewear which can be described as having interchangeable lenses that are held in a partially entrapped configuration. Partially entrapped refers to the condition where the frame is not circumferentially continuous around the edge (also known as profile) of a lens, creating one or more exposed sections of lens edge. Typically, this architecture is seen in the sports eyewear category, but also exists in the realm of Rx glasses and fashion glasses, or various combinations thereof. The frames may either have one lens which covers both eyes, or two independent lenses each covering one eye.
In sporting applications, interchangeability of lenses is desired due to different environmental conditions that the user may encounter. Different environments may warrant different levels of light attenuation and/or color filtration. Photochromatic lenses are available on the market to provide a range of light attenuation with a single lens, but do not offer variation in selective color filtration. Although they are convenient, they do not offer the ideal lens solution for all conditions. Further, fashion also plays a role in lens tint and color selection for many eyewear users. Accordingly, specific independent lenses for specific conditions remain desirable.
In a typical partially entrapped eyewear frame, a lens is attached to a frame via a lens groove interface. The lens groove interface generally includes a section of lens with counter-opposing hook details cut into its profile. The hook details are mated to a lens groove within the eyewear frame which has recesses that receive the lens hooks at or near the extents of the lens groove. Typically the lens fits into the frame with a slight interference fit induced by making the tangential path along the edge of the lens between the hooks to be slightly longer than the corresponding tangential path along the lens groove between the hook recesses. Thus, in a frame of this design, a lens generally cannot be freely installed in or removed from a frame. Specifically, the frame and/or lens must be deformed to overcome the interferences at the lens hooks or the constraining walls of the lens groove. While this is a feasible means to install and uninstall lenses, this may not be desirable from a user's point of view. It is often physically difficult to perform this task and leaves the user concerned that damage is being done to the eyewear. Also, the consumer is likely to grip the optical surfaces of the lens while installing it which can lead to fingerprinting and/or scratching the lens.